Tests

Implemented generic multimodal chat handler. #916

Job	Run time
build-and-test (macos-15-intel, 3.14, -DLLAMA_METAL=off -DCMAKE_OSX_DEPLOYMENT_TARGET=13.3, (No M...	7m 0s
build-and-test (macos-26, 3.14, -DLLAMA_METAL=on -DGGML_METAL_USE_BF16=on -DGGML_METAL_EMBED_LIBR...	2m 44s
build-and-test (windows-2022, 3.14)	8m 2s
build-and-test (windows-2022, 3.9)	9m 28s
build-and-test (ubuntu-latest, 3.14)	3m 33s
build-and-test (macos-15-intel, 3.9, -DLLAMA_METAL=off -DCMAKE_OSX_DEPLOYMENT_TARGET=13.3, (No Me...	7m 48s
build-and-test (ubuntu-latest, 3.9)	3m 31s
build-and-test (macos-26, 3.9, -DLLAMA_METAL=on -DGGML_METAL_USE_BF16=on -DGGML_METAL_EMBED_LIBRA...	3m 2s
	45m 8s

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